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    <script>
        var F = function () { };
        Object.prototype.a = function () {
            console.log('a');
        };
        Function.prototype.b = function () {
            console.log('b');
        }

        var f = new F();
        f.a();  // a
        // 因为f.__proto__是F.prototype，而f.__proto__.__proto__是Object.prototype
        // 因此，访问不到Function.prototype
        f.b();  // 报错
        F.a();  // a 
        F.b() // b
    </script>
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